Disk drive employing spindle motor commutation time variation for reducing acoustic noise

A disk drive that incidentally generates undesirable acoustic noise during an operation mode, the disk drive comprising:

• a spindle motor having a plurality of windings and a rotor rotatable at an operating spin-rate during the operation mode of the disk drive;
• switching elements;
• a commutation state sequencer including a sequence of commutation states for generating a sequence of control signals, the sequence of commutation states including a present commutation state and a next commutation state;
• the switching elements being responsive to the sequence of control signals for sequentially applying a voltage across a selected combination of the windings to generate a torque on the rotor in order to maintain the operating spin-rate;
• a spindle motor control system for providing a series of commutation clock pulses to advance the commutation state sequencer from the present commutation state to the next commutation state, the series of commutation clock pulses having a corresponding series of commutation clock periods, at least two of the commutation clock periods each having a systematically introduced variation from a nominal commutation clock period that depends on the operating spin-rate;
• and
• whereby the systematically introduced variation for each of the at least two commutation clock periods reduces the acoustic noise in the disk drive.